The present invention relates to industrial organic synthesis, specifically to production of phenol and acetone by the cumene method.
A well-known method for the production of phenol and acetone by oxidation of cumene with atmospheric oxygen, followed by the acid-catalytic decomposition of cumene hydroperoxide permits both end products to be produced with high yield (see, for example, Kruzhalov B. D., Golovanenko B. N., Combined Production of Phenol and Acetone, Moscow, Goskhimizdat, 1964, or Kirk-Othmer Encyclopedia of Industrial Chemistry). This method is widely used to produce these products and is the principal technique used in world practice.
Methods are known for producing phenol and acetone in which, to reduce the yield of phenol tar, cumene oxidation products containing cumene hydroperoxide (CHP), cumene, and dimethylphenylcarbinol (DMPC) cleavage in the presence of sulfuric acid to be separated in two stages. In the first stage, at a temperature of 55 to 80° C., most of the CHP (97 to 99%) is decomposed and dicumyl peroxide (DCP) is synthesized from DMPC and CHP. In the second stage, acetone is added and the process fulfilled at a temperature of 80 to 146° C. to the obtained reaction mixture containing phenol, acetone, and alpha-methylstyrene, decomposing DCP and the remaining CHP and DMPC. The addition is made in an amount of 1.5 to 1.8 times the original concentration of acetone. Water is also added. In some cases the acid is partially neutralized with ammonia before the second separation stage in order to ensure optimal acidity of the catalyst. Breakdown of DCP formed in the first stage, decomposition of the remaining CHP and dehydration of the remaining DMPC occur here (See, for example, Russian Patent Nos. 2068404, 2121477, 2142932).
These methods significantly reduce the amount of formed byproducts in comparison with decomposition in one stage, whereas the amount of formed byproduct (hydroxyacetone) remains at a high level (and sometimes increases).
Hydroxyacetone is a source of formation of 2-methylbenzofuran, which is difficult to separate from phenol and which causes deterioration in the color indices of the commercial phenol. Elimination of hydroxyacetone from phenol by alkaline treatment complicates the process (Vasil'eva I. I., Zakoshanski V. M., Petroleum Processing and Petrochemistry, St. Petersburg, “Giord”, 2005, page 344).
The use of a two-stage method to decompose CHP improves the process indices for the synthesis of phenol and acetone, but is associated with the use of a large amount of equipment in comparison with a one-stage CHP decomposition process, and is technically more complicated. For this reason, a large number of installations that use CHP decomposition in one stage continue to be operated. For example, according to U.S. Pat. No. 4,246,203, CHP decomposition is carried out in one stage at a temperature from 120 to 200° C., and almost all of the reaction mass is evaporated using the heat of the decomposition reaction. The best catalyst is sulfuric acid, which is fed to the CHP decomposition reactor in the form of a solution in acetone, acetophenone, cumene or their mixtures, with a concentration from 0.005 to 0.2% (50 to 2000 parts per million (ppm)). The acid concentration in the reaction mass is not mentioned, but it should be higher since the acid remains in the non-volatile residue after evaporation of the reaction products of CHP decomposition.
The method closest to the proposed method for the production of phenol and acetone by acid-catalyzed decomposition of cumene hydroperoxide (CHP), and the simplest technology, is the method described in U.S. Pat. No. 3,271,457. According to the patent, CHP decomposition to phenol and acetone occurs in a reactor to which CHP and catalyst (acid) are fed in an amount at which the acid concentration in the reaction mass is from 0.05 to 10%, preferably from 0.1 to 2%. A mixing/distributing device is installed in the vapor phase above the surface of the reaction mass in which the CHP-containing feedstock is mixed with acetone that is evaporated from the heat of reaction of CHP decomposition on entering the reactor, then condensed in a condenser, and sent back to dilute the feedstock. Thus, the heat released during the reaction is removed and CHP is diluted, which increases the process safety. The process of CHP decomposition is run at a temperature from 50 to 90° C., preferably 70 to 85° C. With this process scheme, there is a significant acetone excess in the CHP decomposition zone in comparison with the stoichiometric ratio of phenol/acetone, and also a very high concentration of acid. The result of this approach is a high yield of hydroxyacetone, the presence of which causes a deterioration in the quality of the commercial phenol.